3,867 research outputs found
Gradient Flow in Logarithmic Conformal Field Theory
We establish conditions under which the worldsheet beta-functions of
logarithmic conformal field theories can be derived as the gradient of some
scalar function on the moduli space of running coupling constants. We derive a
renormalization group invariant version of this function and relate it to the
usual Zamolodchikov C-function expressed in terms of correlation functions of
the worldsheet energy-momentum tensor. The results are applied to the example
of D-brane recoil in string theory.Comment: 12 pages LaTeX; references updated, one added; to be published in
Physics Letters
Signature Gathering in the Initiative Process: How Democratic Is It?
Signature Gathering in the Initiative Process: How Democratic Is It
Signature Gathering in the Initiative Process: How Democratic Is It?
Signature Gathering in the Initiative Process: How Democratic Is It
The Mass Assembly Histories of Galaxies of Various Morphologies in the GOODS Fields
We present an analysis of the growth of stellar mass with cosmic time
partitioned according to galaxy morphology. Using a well-defined catalog of
2150 galaxies based, in part, on archival data in the GOODS fields, we assign
morphological types in three broad classes (Ellipticals, Spirals,
Peculiar/Irregulars) to a limit of z_AB=22.5 and make the resulting catalog
publicly available. We combine redshift information, optical photometry from
the GOODS catalog and deep K-band imaging to assign stellar masses. We find
little evolution in the form of the galaxy stellar mass function from z~1 to
z=0, especially at the high mass end where our results are most robust.
Although the population of massive galaxies is relatively well established at
z~1, its morphological mix continues to change, with an increasing proportion
of early-type galaxies at later times. By constructing type-dependent stellar
mass functions, we show that in each of three redshift intervals, E/S0's
dominate the higher mass population, while spirals are favored at lower masses.
This transition occurs at a stellar mass of 2--3 times 10^{10} Msun at z~0.3
(similar to local studies) but there is evidence that the relevant mass scale
moves to higher mass at earlier epochs. Such evolution may represent the
morphological extension of the ``downsizing'' phenomenon, in which the most
massive galaxies stop forming stars first, with lower mass galaxies becoming
quiescent later. We infer that more massive galaxies evolve into spheroidal
systems at earlier times, and that this morphological transformation may only
be completed 1--2 Gyr after the galaxies emerge from their active star forming
phase. We discuss several lines of evidence suggesting that merging may play a
key role in generating this pattern of evolution.Comment: 24 pages, 1 table, 8 figures, accepted for publication in Ap
HST Observations of Gravitationally Lensed Features in the Rich Cluster Ac114
Deep Hubble Space Telescope images of superlative resolution obtained for the
distant rich cluster AC114 (z=0.31) reveal a variety of gravitational lensing
phenomena for which ground-based spectroscopy is available. We present a
luminous arc which is clearly resolved by HST and appears to be a lensed z=0.64
sub-L star spiral galaxy with a detected rotation curve. Of greatest interest
is a remarkably symmetrical pair of compact blue images separated by 10 arcsec
and lying close to the cluster cD. We propose that these images arise from a
single very faint background source gravitationally lensed by the cluster core.
Deep ground-based spectroscopy confirms the lensing hypothesis and suggests the
source is a compact star forming system at a redshift z=1.86. Taking advantage
of the resolved structure around each image and their very blue colours, we
have identified a candidate third image of the same source roughly 50 arcsec
away. The angular separation of the three images is much larger than previous
multiply-imaged systems and indicates a deep gravitational potential in the
cluster centre. Resolved multiply-imaged systems, readily recognised with HST,
promise to provide unique constraints on the mass distribution in the cores of
intermediate redshift clusters.Comment: submitted to ApJ, 6 pages (no figures), uuencoded Postscript,
compressed TAR of Postscript figures available via anonymous ftp in
users/irs/figs/ac114_figs.tar.gz on astro.caltech.edu. PAL-IRS-
The Density Profiles of Massive, Relaxed Galaxy Clusters. I. The Total Density Over Three Decades in Radius
Clusters of galaxies are excellent locations to probe the distribution of
baryons and dark matter (DM) over a wide range of scales. We study a sample of
seven massive, relaxed galaxy clusters with centrally-located brightest cluster
galaxies (BCGs) at z=0.2-0.3. Using the observational tools of strong and weak
gravitational lensing, combined with resolved stellar kinematics within the
BCG, we measure the total radial density profile, comprising both dark and
baryonic matter, over scales of ~3-3000 kpc. Lensing-derived mass profiles
typically agree with independent X-ray estimates within ~15%, suggesting that
departures from hydrostatic equilibrium are small and that the clusters in our
sample (except A383) are not strongly elongated along the line of sight. The
inner logarithmic slope gamma_tot of the total density profile measured over
r/r200=0.003-0.03, where rho_tot ~ r^(-gamma_tot), is found to be nearly
universal, with a mean = 1.16 +- 0.05 (random) +0.05-0.07
(systematic) and an intrinsic scatter of < 0.13 (68% confidence). This is
further supported by the very homogeneous shape of the observed velocity
dispersion profiles, obtained via Keck spectroscopy, which are mutually
consistent after a simple scaling. Remarkably, this slope agrees closely with
numerical simulations that contain only dark matter, despite the significant
contribution of stellar mass on the scales we probe. The Navarro-Frenk-White
profile characteristic of collisionless cold dark matter is a better
description of the total mass density at radii >~ 5-10 kpc than that of dark
matter alone. Hydrodynamical simulations that include baryons, cooling, and
feedback currently provide a poorer match. We discuss the significance of our
findings for understanding the assembly of BCGs and cluster cores, particularly
the influence of baryons on the inner DM halo. [abridged]Comment: Updated to matched the published version in Ap
Subaru Weak Lensing survey -- II: Multi-object Spectroscopy and Cluster Masses
We present the first results of a MOS campaign to follow up cluster
candidates located via weak lensing. Our main goals are to search for spatial
concentrations of galaxies that are plausible optical counterparts of the weak
lensing signals, and to determine the cluster redshifts from those of member
galaxies. Around each of 36 targeted cluster candidates, we obtain 15-32 galaxy
redshifts. For 28 of these targets, we confirm a secure cluster identification.
This includes three cases where two clusters at different redshifts are
projected along the same line-of-sight. In 6 of the 8 unconfirmed targets, we
find multiple small galaxy concentrations at different redshifts. In both the
remaining two targets, a single small galaxy concentration is found. We
evaluate the weak lensing mass of confirmed clusters. For a subsample of our
most cleanly measured clusters, we investigate the statistical relation between
their weak lensing mass and the velocity dispersion of their member galaxies,
comparing our sample with optically and X-ray selected samples from the
literature. Our lensing-selected clusters are consistent with
sigma_v=sigma_sis, with a similar scatter to the optically and X-ray selected
clusters. We thus find no evidence of selection bias compared to these other
techniques. We also derive an empirical relation between the cluster mass and
the galaxy velocity dispersion, which is in reasonable agreement with the
prediction of N-body simulations in the LCDM cosmology.Comment: 58 pages, 45 figures, submitted to PASJ. A version with
full-resolution figures is available at
http://th.nao.ac.jp/~hamanatk/PP/supcam_wl2.pd
A Slow Merger History of Field Galaxies Since z~1
Using deep infrared observations conducted with the CISCO imager on the
Subaru Telescope, we investigate the field-corrected pair fraction and the
implied merger rate of galaxies in redshift survey fields with Hubble Space
Telescope imaging. In the redshift interval, 0.5 < z < 1.5, the fraction of
infrared-selected pairs increases only modestly with redshift to 7% +- 6% at
z~1. This is nearly a factor of three less than the fraction, 22% +- 8%,
determined using the same technique on HST optical images and as measured in a
previous similar study. Tests support the hypothesis that optical pair
fractions at z~1 are inflated by bright star-forming regions that are unlikely
to be representative of the underlying mass distribution. By determining
stellar masses for the companions, we estimate the mass accretion rate
associated with merging galaxies. At z~1, we estimate this to be 2x10^{9 +-
0.2} solar masses per galaxy per Gyr. Although uncertainties remain, our
results suggest that the growth of galaxies via the accretion of pre-existing
fragments remains as significant a phenomenon in the redshift range studied as
that estimated from ongoing star formation in independent surveys.Comment: 5 pages, accepted for publication in ApJ Letter
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